[Bldg-sim] Modeling a Green Roof

Sami, Vikram Vikram.Sami at perkinswill.com
Fri Jun 25 08:24:25 PDT 2010


There's also been some interesting research done in California on this.

Here's<http://www.plea2009.arc.ulaval.ca/Papers/2.STRATEGIES/2.2%20Heating%20and%20Cooling/ORAL/2-2-17-PLEA2009Quebec.pdf> a paper published by Pablo La Roche at Cal Poly Pomona
Here's<http://www.plea2009.arc.ulaval.ca/Papers/2.STRATEGIES/2.2%20Heating%20and%20Cooling/ORAL/2-2-18-PLEA2009Quebec.pdf> another out of USC.



Vikram Sami, LEED AP
Sustainable Design Analyst
1382 Peachtree St. NE, Atlanta, GA 30309
t: 404-443-7462    f: 404.892.5823       e: vikram.sami at perkinswill.com   www.perkinswill.com<http://www.perkinswill.com/>
Perkins+Will.  Ideas + buildings that honor the broader goals of society


From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Friday, June 25, 2010 10:41 AM
To: Drury B Crawley; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Modeling a Green Roof

Open question:

I've ascribed to the "tack an R / thermal mass value onto a new  layer" approach in the past... but would appreciate a more nuanced approach if it could be done quickly enough.

I'm curious:  Does EnergyPlus or any other option/model out there account the variable shading effects of the foliage on the roof construction, as a user might define it?  I've speculated this element could be handled relatively simply in eQuest using a geometrically adjacent shading surface with an annual fractional schedule, but eQuest (to my experience) doesn't have a clean approach to account for the varying thermal mass and insulative properties of soil that varies in moisture over time...

~Nick

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NICK CATON, E.I.T.
PROJECT ENGINEER
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
Check out our new web-site @ www.smithboucher.com

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Drury B Crawley
Sent: Friday, June 25, 2010 9:25 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Modeling a Green Roof

EnergyPlus has a model for green roofs built in -- based on experimental measurements and experience of researchers at Portland State University, Prof David Sailor:  http://web.cecs.pdx.edu/~sailor/



---------- Forwarded message ----------
From: Jeremy Poling <jpoling at epsteinglobal.com<mailto:jpoling at epsteinglobal.com>>
Date: Fri, Jun 25, 2010 at 10:04 AM
Subject: Re: [Bldg-sim] Modeling a Green Roof
To: Jason.Boehning at ricegardner.com<mailto:Jason.Boehning at ricegardner.com>, bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Penn State University (http://horticulture.psu.edu/cms/greenroofcenter/) and Michigan State University (http://www.hrt.msu.edu/greenroof/) both have significant research programs on green roofs.  I would recommend looking at the results of the Penn State study on energy transfer in Green Roofs (http://etda.libraries.psu.edu/theses/approved/WorldWideFiles/ETD-4616/Thesis_Paulo_Tabares_revised.pdf).  In general, green roofs handle energy through the insulating effects of soil, the cooling effects of evapotranspiration in the plants, and water flows within the green roof assembly.  This means that a calculated R-value will be different depending on the amount of plant material participating in evapotranspiration, the wetness of the soil, and whether the roof is intensive or extensive.  A straight R-value approach is very simplified and should be used with the understanding that model results are much less likely to be accurate.  The Penn State study gives a review of published literature showing extensive green roofs have R-values between 1.8 and 4.8 while intensive green roofs have R-values between 5 and 20.

In general, the average R-value of soil is 0.25 per inch, so for a 12" soil depth the R-value of the soil would be R-3 excluding assumptions on soil wetness and evapotranspiration.  We typically go conservative and just model the R-value of the additional soil since you would need a TRNSYS or MatLab model to take into account the other energy benefits of a green roof.

JEREMY R. POLING, PE, LEED AP
Associate Vice President,
Senior Sustainability Analyst
Strategic Services
Site Solutions | Operations | Sustainability

EPSTEIN

Epstein is a firm believer in sustainability. We ask that you please consider the environment before printing this e-mail.

From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org>] On Behalf Of Fareed Syed
Sent: Friday, June 25, 2010 8:05 AM
To: Jason Boehning; bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: Re: [Bldg-sim] Modeling a Green Roof

I heard from our director of sustainability to use R-5 for a typical green roof. It was confirmed by few senior architects.

Thanks,

Fareed

From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org>] On Behalf Of Jason Boehning
Sent: Friday, June 25, 2010 8:46 AM
To: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: [Bldg-sim] Modeling a Green Roof

Howdy!

Has anyone modeled a green roof? I have a standard roof with 12 inches of soil and grass. I have been searching the web for thermal properties such as U values, thermal absorptivity and so on. Are there any good references to find these values or does anyone have tips to model a green roof? I appreciate your help.



Jason Boehning, EIT

Mechanical Engineer

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6161 Savoy, Suite 1212
Houston, Texas  77036

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 f.   713.482.2314
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